The present study examined the relationship between smoking during pregnancy and behavior and emotional problems in a community sample of 4-year-old children. This study differed from most prior research in the use of a large, diverse sample, the age of the children participating in the study, the range of psychosocial factors studied, and the use of multiple measures of child psychopathology. The findings having implications for our understanding of the relationship between smoking during pregnancy and child psychopathology, as well as implications for the design of future studies in this area.
First, in the present study, the relationship between smoking during pregnancy and symptoms of ODD in preschoolers was not significant, even without including other risk factors and correlates of smoking during pregnancy. While a small number of other studies of preschool children have reported a significant relationship between smoking during pregnancy and externalizing problems, all (Day et al., 2000
; Huijbregts et al., 2007
; O’Callaghan et al., 1997
; Orlebeke et al., 1997
; Wakschlag & Keenan, 2001
) but one (Wakschlag et al., 2006
) failed to control for at least one covariate in each area of demographic, parental psychopathology, parenting, family stress, and pre-/perinatal factors, and the latter study was limited by a lack of racial/ethnic diversity in the sample. Thus, overall, there is little evidence for a main effect of smoking during pregnancy on oppositional behavior in preschool children.
Second, the present study failed to find a significant relationship between smoking during pregnancy and either ADHD-H or ADHD-C, and the relationship between smoking during pregnancy and ADHD-I was not significant after including a wide range of covariates. While these results differ from prior studies (Huijbregts et al., 2007
; McGee & Stanton, 1994
; Romano et al., 2008
; Streissguth et al., 1984
), those studies failed to include the range of variables included in the present study.
Third, consistent with three prior studies, the present study failed to find a relationship between smoking during pregnancy and internalizing disorders. Collectively, these studied provide little evidence for an association of smoking during pregnancy with these types of disorder.
Fourth, the present study does not support the developmental model proposed by Nigg and Breslau (2007
). That model posited that smoking during pregnancy contributes to temperamentally-based NA in young children which, combined with problems in parent–child relationships, mediates the relationship between smoking during pregnancy and the later development of ODD symptoms. If NA serves as a mediator, then the relationship between the independent variable (smoking during pregnancy) and the mediator (NA) should be statistically significant (Baron & Kenny, 1986
). The results of the present study do not support this model because there was a nonsignificant effect for smoking during pregnancy on NA in young children when controlling for theoretically and empirically related covariates.
However, while the results of the present study do not support a relationship between smoking during pregnancy and behavior problems in preschool children, it is possible that direct effects of smoking during pregnancy on behavior and emotional problems do not emerge until children are school age or older. While ODD in preschoolers is reasonably stable, ODD symptoms do decline in some children at about age 5 years (Lavigne et al., 1998
), and the direct effects of smoking during pregnancy on ODD and other externalizing problems and ADHD might only become apparent among those children with ODD persisting into, or beginning in, the school years.
Finally, the present study demonstrates the importance of including a wide range of variables that are associated with the development of child psychopathology in order to estimate the effects of smoking during pregnancy. While prior studies typically included demographic and child health variables, and often assessed maternal psychopathology and some aspects of family climate, important aspects of mother–child interaction patterns, particularly those required to promote secure attachment, have been ignored. When the full range of variables was included in the present study, reducing the effects of omitted variables, the effects of smoking during pregnancy for ADHD-I that had appeared significant no longer were. This is not entirely surprising. Wakschlag et al. (2002
) had raised concerns about confounding variables in studying the effects of prenatal smoke exposure, concerns about the effects of omitted variables in study psychopathology have been noted before (Tomarken & Waller, 2003
), and the results of the present study are consistent with those predicted by D’Onofrio et al. (2008), who argued that the relationship between smoking during pregnancy and measures of child psychopathology would be associated with environmental risk factors other than those which had been studied previously. The results of the present study suggest a wide range of correlates of prenatal smoke exposure, including child attachment, should be included when studying the effects of smoking during pregnancy.
The two main limitations of the present study involve the use of retrospective reports of smoking and the inability to assess dose effects of exposure to smoking during pregnancy. The present study used the retrospective report of smoking during pregnancy from the Smoke-Free Families clinical trial (Melvin et al., 2000
) and classified the children as exposed versus not exposed. We followed this procedure because our confidence was greater that mothers would more accurately recall whether or not they had smoked during pregnancy than the number of cigarettes they typically smoked at that time, and studies have indicated that maternal recall for smoking during pregnancy is good even over long periods of time. In addition, if the measure used in the present study was not at all valid, then significant correlations between many of the known psychosocial correlates of smoking and prenatal smoke exposure obtained with the measure used in the present study would not have been significant. However, contemporaneous reports of smoking during pregnancy are still to be preferred to retrospective reports. The “caveat” to be taken from this report is that a wide range of psychosocial correlates needs to be included in future studies on the effects of smoking during pregnancy when contemporaneous or retrospective measures of smoking are used.
A second major limitation concerns the possibility of dose effects. Most studies of compared exposed to unexposed children, other studies have identified a dose effect, with behavior problems emerging if mothers were relatively heavier smokers. Since the present study did not examine dose effects, it is possible that there is a dose effect for smoking during pregnancy not detected in the present study. The most important finding of the present study is that, since the inclusion of the wide range of psychosocial variables, particularly parenting variables and attachment, examined in the present study showed no effect of prenatal smoke exposure versus non-exposure, future studies of dose effects for prenatal smoke exposure need to examine these same critical variables to be definitive. Thus far, studies (Ashford et al., 2008
; Button, Thapar, & McGuffin, 2005
; D'Onofrio et al., 2008
; Day et al., 2000
; Fergusson, Horwood, & Lynskey, 1993
; Fergusson, Woodward, & Horwood, 1998
; Maughan, Taylor, Caspi, & Moffitt, 2004
; Silberg et al., 2003
; Streissguth et al., 1984
; Thapar, Fowler, Rice, & al., 2003
; Wakschlag et al., 2006
; Weitzman et al., 1992
; Williams et al., 1998
) showing a dose-effect relationship with stronger effects for heavier prenatal smoke exposure have failed to do this, so the problem of “omitted variables” in dose-effect studies remains. Future studies of dose-effect relationships need to include a sufficiently broad representation of psychosocial factors associated either with smoking or the development of behavior problems to assess the strength of the relationship between smoking during pregnancy and child psychopathology.
A third limitation involves the use of a single parent informant for many of the risk factors. The use of a single informant increases the possibility that significant results are inflated due to common method variance. However, this was certainly not the case in the present study because the main findings involved an absence of significant relationships between the variables, so it is unlikely that inflated effects sizes due to common method variance significantly impacted the results. Also, in addition to maternal-report, we used direct observation to examine several of the risk variables included in this study (i.e., parent scaffolding, child attachment).
The strengths of this study include attention to preschoolers, the wide range of covariates studied, the assessment of both externalizing and internalizing disorders in young children, the use of multiple measures of outcome rather than reliance upon a single measure, and the inclusion of a large, diverse community sample. These results highlight the importance of carefully selecting theoretically relevant, empirically tested variables that may serve as mediators in the relationship between smoking during pregnancy and child internalizing and externalizing problems. This is consistent with current approaches in developmental psychopathology, in which researchers are turning their attention to the interaction between biological and psychosocial variables as causal factors in child disorders, rather than focusing on only one of these aspects of human functioning (Cicchetti & Curtis, 2007